Ζ. Kristallogr. NCS 216 (2001) 25-26 25
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Crystal structure of cesium ortho-tellurosilicate, Cs4SiTe4
J. Schlirf* and H. J. Deiseroth
Universität Siegen. Anorganische Chemie. D-57068 Siegen. Germany
Received July 25. 2000. CSD-No. 409511
109.5
Abstract
Cs4SiTe4, cubic, P43n (No. 218), a = 15.081(2) Ä, V = 3430.0 λ3, Ζ = 8, Rgi(F) = 0.032, wR,ef<F2) = 0.057, Τ = 2 9 3 Κ.
Source of material
The title compound was prepared starting from an inhomo- geneous sample obtained by thermal decomposition of CsN3 mixed with a prereacted mixture of SiTe2 and Te (molar composi- tion 6 Cs: 2 Si: 6 Te) at 640 Κ in a quartz glass ampule. The raw product was heated to 920 K. After quenching in icewater, ho- mogenization and subsequent annealing at 790 Κ for 16 days the reaction yielded air sensitive, transparent, red-orange single crys- tals of Cs4SiTe4. An additional phase must be present, but could not be identified up to now.
Discussion
Cs4SiTe4 is the second example of a crystalline solid with the composition M4M'X4 prepared using the "azide-method" [1].
Compounds with the composition M4M'X4 (M = alkali metal) are well known for Μ = Li (M' = Ge, X = S), Na (M' = Ge, X = S, Se;
M' = Sn, X = S, Se, Te), Κ (Μ' = Sn, Χ = Se, Te), Rb (M' = Sn, X = Se, Te) and Cs (M' = Sn, X = S, Se; M' = Si, X = Se) [2,3,4], They crystallize in six different structure types characterized by iso- lated M'X4-tetrahedra and coordination numbers between 4 and 7 for the alkali metals. Cs4SiTe4 crystallizes like Cs4SiSe4
isotypically to Ba4SiAs4 [5]. In this structure, cesium atoms are embedded in a matrix of SiTe4-tetrahedra (<i(Si—Te) = 2.51 Ä and 2.52 Ä) and show a distorted octahedral coordination of tellu- rium atoms (d(Cs—Te) = 3.84 A - 3.94 Ä). Whereas ideal 7d-symmetry is observed for the Si( 1 )Te4-tetrahedra, the Si(2)Te4 are distorted with Te-Si-Te angles of 107.3° and 114.0°, respectively (see fig.). The spatial distribution of the Si( 1) and Si(2) atoms centering the SiTe4-tetrahedra is topologically equivalent to the A l 5 structure type (CnSi) with Si(l)Te4 corre- sponding to Si and Si(2)Te4 corresponding to Cr.
Table 1. Data collection and handling.
Crystal:
Wavelength:
μ:
Diffractometer, scan mode:
29max-
WlWJmeasured. N(hkl)mjque: Criterion for l0bs, N(hkl)&: iVfparam.) ref,ned:
Programs:
red-orange, transparent, wedge shaped fragment, size 0.04 χ 0.08 χ 0.10 mm Mo Ka radiation (0.71069 Ä) 151.30 cm"'
STOEIPDS, φ 50.02°
27171,1016 /obs > 2 a(/ot>J, 818 28
SHELXS-97 [6], SHELXL-97 [7], DIAMOND [8]
Table 2. Atomic coordinates and displacement parameters (in A2).
Atom Site X y Ζ Uu Uu i/33 Uu Uu t/23
Cs(l) 24/ 0.15071(6) 0.41304(6) 0.36608(5) 0.0342(5) 0.0338(5) 0.0351(5) -0.0016(4) 0.0030(3) 0.0023(4)
Cs(2) 8<? 0.15112(6) X X 0.0359(3) Uu Uu -0.0035(4) Un Un
Si(l) 2 a 1/2 1/2 1/2 0.018(2) Uu Uu 0 0 0
Si(2) 6c 1/4 1/2 0 0.017(3) Uu Uu 0 0 0
Te(l) 24/ 0.15896(6) 0.40755(6) 0.10527(5) 0.0311(5) 0.0295(5) 0.0259(4) -0.0055(4) 0.0054(4) 0.0065(3)
Te(2) 8? 0.40385(6) X X 0.0298(3) Uu UM -0.0054(3) U12 Un
* Correspondence author (e-mail: schlirf@chemie.uni-siegen.de)
26 Cesium ortho-tellurosilicate
Acknowledgment. This work was supported by the Deutsche Forschungs- gemeinschaft.
References
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